The present invention relates to saw chain sharpening apparatus, and more particularly to those forms of saw chain sharpening apparatus using a power-driven rotary grinding wheel mounted on a motor arm, the motor arm being shiftable so that the grinding wheel may be positioned for sharpening right and left-hand cutting teeth of a saw chain without removing the saw chain from a clamping device. The present invention is directed to improvements in such apparatus, and more particularly is concerned with providing a self-centering saw chain clamping device which will substantially align and maintain, independently of width, a saw chain's lengthwise centerline on a preselected datum line. Also, the present invention is directed towards providing an improved configuration for offsetting a grinding wheel with respect to the preselected datum line.
Saw chain grinding apparatus which employ a power-driven rotary grinding wheel mounted on a motor arm movable along a base-mounted arcuate guide are known in the art. These devices typically employ a base mounted saw chain clamping or gripping construction which is used to maintain a segment of a saw chain in position for sharpening by the grinding wheel. Associated with the clamping or gripping device is an indexing arm or finger which serves to prevent a saw chain cutting tooth from being moved in one direction while the grinder is used to sharpen the tooth. The grinding wheel, being movable along an arcuate slot, may be first positioned at a preselected location on the arcuate guide for sharpening the right-hand cutting teeth. The wheel is then moved along the arcuate guide to a second position for sharpening the left-hand cutting teeth. The saw chain is indexed along the gripping or clamping device without the necessity of removal therefrom.
A problem present with the prior art saw chain grinding apparatus as described above resides in the fact that the length-wise centerline of a saw chain will not be maintained at a fixed location with respect to the grinding wheel if saw chains of differing widths are successively used in the apparatus. In sharpening right and left-hand cutter elements, it is important that each element be ground uniformly throughout the length of the saw chain. In the prior art, such uniformity was ensured for a saw chain of a particular width by setting the grinder at the factory or by providing clamps which had to be reset for each chain width to be sharpened. However, if an operator in the field desired to sharpen a saw chain having a width different from that accommodated by the factory setting the operator took the chance of imprecisely setting the apparatus.
The present invention overcomes the aforementioned problem by providing a self-centering clamping device which substantially aligns and maintains the lengthwise centerline of a saw chain on a preselected datum line without regard to the saw chain's width. The preselected datum line is intersected by a fixed, reference axis which is the axis about which the motor arm mounting bracket is angularly displaced along the arcuate guide. Because a saw chain's lengthwise centerline is substantially aligned and maintained along the preselected datum line, and because such datum line intersects a reference axis, the position of the grinding wheel with respect to either right or left-hand cutter elements of a saw chain supported in the self-centering clamping device is maintained constant. Thus, it may be readily appreciated that a sharpening operation will proceed uniformly on the cutting elements.
The prior art saw chain sharpening apparatus also presents another problem in that the apparatus must be adjusted through various complicated mechanism to sharpen cutting teeth other than the so-called Oregon type teeth. For instance, it is common to use a grinding apparatus to sharpen micro, semi or super chisel-type saw chain teeth. In order to sharpen such chisel-type teeth, it is necessary to grind such a tooth across the full width thereof. Such full width sharpening requires that the centerline of a rotary grinding wheel be adjusted with respect to the centerline of a supported saw chain length. In order to alter the position of a grinding wheel's centerline with respect to the lengthwise centerline of a supported saw chain, as when changing from sharpening Oregon cutter teeth to sharpening chisel-type teeth, it is desirable to provide axes offset from the reference axis about which the motor arm mounting bracket travels. By providing such offset axes, the relative positions of a centerline of a grinding wheel and the lengthwise centerline of a saw chain may be appropriately adjusted.